1. FIELD OF THE INVENTION
The present invention relates to a process for the manufacture of multilayer impermeable strips for use, for example, in the building industry, particularly for making damp proof floors. Multilayer strips of this nature are commonly used for this purpose and, thus, the object of this invention is a system for making said strips and which offers certain advantages allowing the disadvantages ordinarily encountered in the diverse stages of the process to be overcome.
2. PRIOR ART
Various laminating procedures are disclosed the prior art. Thus, Harris U.S. Pat. No. 3,620,878 discloses the formation of a "sandwich" construction in which a foam sheet is laminated, by an adhesive, to a heat-shrinkable film to provide a heat-shrinkable cushioning structure. The foam material and the film material are fed between a press roll and a chill roll, and adhesive is extruded between the foam and the film into the "nip" therebetween. While this patent discloses direct chilling at the adhesion point, it is not capable of solving the technical problems involved in manufacturing multi-layer impermeable strips such as formed by the present invention, as, using the Harris procedure, the thin layers of plastic material would not properly adhere to the thick molten asphalt.
Addison U.S. Pat. No. 3,698,980 initially applies asphalt to paper after which a polypropylene fabric is applied to the asphalt. The polypropylene is in the form of woven strands which are longitudinally oriented, and the resultant laminated material is attended as a fabric wrapping material. In Addison, the propylene fabric must be thicker than the plastic layer used in the procedure of the present convention and the fabric structure absorbs the retractions caused by heating. Furthermore, the paper used in Addison has a greater dimensional stability than does plastic as it is not subject to molecular orientation phenomena and is not subject to transitions. The wrapping material produced by the Addison procedure cannot be used as a water-proof covering for roofs, terraces and the like, and thus is disadvantageous from the standpoint of the type of material intended to be produced by the process of the present invention.
Benson U.S. Pat. No. 3,252,851 is directed to the production of a membrane liner in the form of an impermeable sheet material which may be used as a water and vapor barrier membrane in certain types of constructions and also as a water-retaining liner in other types of constructions. In Benson, short intervals are left between the application of hot asphalt to plastic films and the cooling of the films, and this is disadvantageous from the standpoint of producing impermeable strips in a continuous process as in the present invention.
Pecker U.S. Pat. No. 2,989,414 discloses a method of imparting dimensional stability to felt back surface coverings, in which a water filmed roller is used for the purpose of affecting the introduction of a controlled amount of water into a coated web. The material is cooled prior to the action of rolling the material with a roll dipped in water. The procedures suggested by Pecker are inapplicable to a process for manufacturing impermeable strips formed by a plurality of layers in a continuous process and useful in particular for making damp-proof floors.
Above U.S. Pat. No. 2,893,907 teaches principally the product to be prepared, which is admitted as known in the present invention, but it does not teach any similar manufacturing process.
As distinguished from the prior art procedures mentioned above, the present invention concerns a process for the manufacture of waterproof sheets for use in the building trade, particularly for waterproofing of floors. In order better to perform their function and, at the same time, to facilitate their application, these waterproof sheets are usually compound sheets, formed by very thin plastic sheets alternating with substantially thicker asphalt layers, the simplest waterproof sheet being formed of two outer plastic sheets and an inner asphalt layer. The asphalt layer may consist of asphalt only or it may be an asphalt mixture containing 65-70% asphalt, 25-30% slate shale and 5-10% of latex or a latex-type elastomer.
In these compound sheets, apart from its adhesive function, the asphalt or asphalt mixture has also the more important function of waterproofing. In order to fulfill this function, the asphalt or asphalt mixture must be substantially thicker than the necessary minimum thickness for adhesive purposes.
In order to form the asphalt or asphalt mixture into a sheet layer and bind it to the adjacent plastic sheets, it is necessary to melt it and bring it into contact with the plastic sheets but, since the melting temperature of the asphalt is normally higher than that of the plastic sheets, the important problem arises, in this operation, of avoiding the melting of the plastic sheets when they contact the molten asphalt. This problem is less important when the asphalt layer is thin with respect to the plastic sheets used, since in such case the heat contained in the asphalt layer and partially transferred to the plastic sheets is not sufficient to cause melting of the plastic and may be removed with delayed refrigeration, such as happens in U.S. Pat. Nos. 2,989,414; 3,252,851 and 3,698,980.
The problem solved by the present invention is serious. The essence of the invention resides in the fact that a simple pair of compression rollers performs the following operations simultaneously: (a) rolling of the molten asphalt or asphalt mixture; (b) bonding of the asphalt or asphalt mixture to the adjacent plastic sheets and (c) cooling of these sheets precisely at the time and place when and where they contact the molten asphalt or asphalt mixture, by way of layers of water picked up by the rollers as they turn.
What is really an achievement of the present invention is to obtain a thick strip (about 4 mm thick) having two very thin layers (0.02 to 0.09 mm thick) of an extremely flexible material (polyethylene) and a thick layer of asphalt placed between them. This is not easily done, since the asphalt does not easily adhere to the polyethylene. The process of the invention makes it possible to obtain a perfect adhesion in such a type of strip, in which the proofing base is the plastic layers, whereas the thick asphalt layer acts both as a protective and as adhesive.